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Article

Record of Mid-Eocene Warming Events in the Istrian Paleogene Basin, Neotethys (Outer Dinarides, Croatia)

by
Ines Galović
1,
Đurđica Pezelj
2,
Renata Lukić
2,
Katja Mužek
1,2,
Krešimir Petrinjak
1,
Marija Horvat
1,* and
Vlasta Ćosović
2
1
Croatian Geological Survey, 10000 Zagreb, Croatia
2
Department of Geology, Faculty of Science, University of Zagreb, 10000 Zagreb, Croatia
*
Author to whom correspondence should be addressed.
Geosciences 2025, 15(9), 366; https://doi.org/10.3390/geosciences15090366
Submission received: 11 June 2025 / Revised: 11 July 2025 / Accepted: 22 August 2025 / Published: 16 September 2025
(This article belongs to the Special Issue Mesozoic-Palaeogene Hyperthermal Events)
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Abstract

Several short sections from Istria (northern Adriatic Sea) were studied to determine the impact of short-term climate variability on pelagic assemblages from the northern mid-latitudes during a critical period of evolution in the mid-Eocene greenhouse climate. Two important warming events were documented in this interval—the Late Lutetian Thermal Maximum (LLTM) and the Middle Eocene Climate Optimum (MECO). The warmings were characterised by the highest calcareous nannofossil species richness and an eutrophic environment. Our records of calcareous nannofossil index species allowed the standard Zones NP16–NP17 (Mediterranean Subzones MNP16A–MNP17A) to be applied. Common occurrences of the planktonic foraminiferal genera Subbotina and Turborotalia indicate eutrophic-to- mesotrophic conditions between the mixed layer and the shallow thermocline waters in the basin. Episodes of eutrophication from periodic upwelling under an accelerated warming event (in MNP16A) are indicated by the subdominant Coccolithus pelagicus. According to the isotope data, the maximum negative δ13C occurred at 45° N in Alano, with a prominent second peak at 39.66 Ma, which is in agreement with our possible second peak, suggesting higher insolation in the North during the warming event. The warm water Reticulofenestra producta dominated in Subzone MNP17A, suggesting a relatively shallow mesotrophic environment with decreased species richness characteristic of the post-MECO phase.

1. Introduction

The middle Eocene (48.0–37.7 Ma) pelagic sediments of the high-southern-to-low-northern-latitude open ocean have been well studied [1,2,3,4]. This warmhouse period was punctuated with at least two transient global warming events. The short-lived (30 kyr) Late Lutetian Thermal Maximum (LLTM), also known as the Chron C19r hyperthermal event, at 41.52 Ma was characterised by ~2 °C warming of the deep ocean in the South Atlantic when an even higher insolation value (573 W/m2) was recorded at 65° N [5,6,7]. The LLTM can be recognised as a drastic carbonate dissolution interval with an iron (Fe) intensity peak in the northern Atlantic low latitudes [8] while in the southern mid-latitudes, it is an interval with a higher carbonate content but pronounced Fe peaks [9]. Reference [7] determined high insolation values of ~560 W/m2 at 41.913 Ma in the Northern Hemisphere (65° N) 0.4 Myr earlier, which coincided with a maximum in the 1.2 Myr obliquity cycle. The maximum eccentricity led to very warm summers, causing the LLTM, but this has not been recognised geochemically or isotopically because of drastic carbonate dissolution in the northern Atlantic. The high release of carbon (C) from the oxidation of terrestrial/marine organic matter may have caused a C isotope excursion (CIE), especially in combination with exceptionally high northern insolation, which induced significant biosphere productivity [9]. The evidence of ecological disturbances is recorded both in foraminiferal assemblages and calcareous nannofossils. During this interval, peri-Tethyan planktonic foraminiferal assemblages have shown increased abundances of mixed-layer muricate acarininids and morozovelloidids [10]. In addition, peaks in the abundance of opportunistic benthic foraminifera and the small calcareous nannofossil Reticulofenestra, alongside a reduction in the abundance of the oligotrophic calcareous nannofossil Zygrhablithus bijugatus, were reported from the eastern Atlantic continental margin at this time [11]. In the South Atlantic, studies on smaller benthic foraminiferal assemblages suggest changes in the species abundances, like Bulimina elongata, which correlate with a negative carbon isotope excursion [12]. The predominance of reticulofenestrids has been recorded from this interval in the western Neotethys [13] and the northwestern Pacific [14], while sphenoliths were predominant in the South Atlantic and Tunisian Dorsal [15,16].
The second warming event in the middle Eocene is the Middle Eocene Climatic Optimum (MECO) (~40.0 Ma; lasted ~500 kyr). During this period, the long-term cooling trend was interrupted, and global temperatures were ~3–6 °C warmer than before the event [1,4,17] in both surface and intermediate ocean waters. This was followed by a rapid 200 kyr cooling period [18]. Latitudinal temperature gradients point to an uneven distribution of heat at the Earth’s surface that manifested as variations in ecosystems and an extreme hydrological cycle [9,19]. The changes recorded in the mid-Eocene generally involved ocean stratification, acidification, and nutrient supply cycles, which affected marine phytoplankton productivity and, consequently, microfauna productivity, especially in terms of calcifying microfossils [17,18,20] with some exceptions like in the southeast Atlantic, which has no CIE record [1]. The shift from oligotrophic to eutrophic conditions that occurred in some places, as evidenced by increased abundances of planktonic subbotinids and low-oxygen pseudohastigerinids [21], suggests increased nutrient input and productivity in the surface ocean associated with the MECO event. The effects were also evident in the calcareous nannofossil record, with an increase in reticulofenestrids found in the central Neotethys, confirming the enhanced eutrophic conditions [16,22] that prevailed globally during the CIE [9]. The recently described MECO warming peak recorded the most dramatic biotic changes, such as a peak in eutrophic calcareous nannofossils, a disappearance (at least at in the upper part of the MECO, [23,24,25] of oligotrophic large planktonic foraminifera (like Acarinina, Morozovelloides,) and a peak in deep-dweller Subbotina [22,25]. The post-MECO phase was characterised by abruptly decreasing temperatures (by ~3 °C) following the peak warming. This occurred globally within 50 kyr, covering the time interval up to 39.3 Ma in the North Atlantic [18]. The warm conditions occurred alongside fluctuating nutrient and productivity levels in the Neotethys [22].
The subsequent post-MECO rapid cooling period witnessed a progressive reduction in abundances of the characteristic Eocene planktonic foraminifera surface dwellers, which hosted algal photosymbionts in the western North Atlantic [26,27,28,29]. This decline coincided with a reduction in their morphological and structural complexity in the Indo-Pacific [30]. The same scenario occurred in the Neotethys, with a notable increase in abundances of Globigerinatheka and Subbotina [22]. These species likely filled the ecological niches left vacant by the decrease in morozovelloidids and acarininids. Oligotrophic nannoplankton, such as the sphenoliths, dominated in the South and North Atlantic, whereas in the central Neotethys, there was an increase in eutrophic and mesotrophic reticulofenestrids, as observed in [15], similarly to the pre-MECO phase [22].
Little is known about the response of the planktonic community to rapid climate change in marginal seas. To date, the MECO has been studied in detail in land sections—the Alano, Contessa, Monte Cagenero, Ligurian area (Capo Mortola, Oliveta San Michele, and Sealza) and Tunisian Dorsal sections in the central western Neotethys [15,21,23,24,25,31,32,33], the Belaya River section in the Peri-Tethys area [22,34] and the Baskil section in the central eastern Neotheys [23]—while the LLTM has only been found in the Ainsa and Contessa sections, along with the probably slightly earlier C19r event [35,36].
Here, we present data on calcareous nannoplankton and planktonic foraminifera from sediments deposited in a mid-latitude marginal basin in the central Neotethys. To better constrain age, we combined biostratigraphic data from calcareous nannoplankton and planktonic foraminifera from several short sections in the northwestern Adriatic flysch basin (Figure 1). We correlated biostratigraphy with the stable C isotopes (δ13C) from bulk carbonates from the same interval with regional and global data to emphasis possible aforementioned discrepancies between the north and south latitudes during the warming periods. In addition, geochemical parameters were used to reconstruct/confirm the palaeoenvironment of the C19r and MECO events in the marginal sea of the Neotethys, which was deposited in a terrestrially influenced shallow basin 900–1200 m deep [37].

2. Materials and Methods

The studied sections were exposed in the Pazin Basin, Istrian Peninsula (Outer Dinarides, Croatia). We were particularly interested in studying the oldest marly sequences within the flysch succession, so we focused on the marly interval above the foraminiferal limestones (shallow water carbonates). The marls of four short sections (~2–10 m thick) of flysh sediments were studied from the Istrian Paleogene Basin in the Neotethys (Figure 1, with—two at Jakomići (Jakomići I [J], 45.209153° N, 14.0508517° E and Jakomići II [JAK], 45.212595° N, 14.05088° E) and one each at Racani (RAC, 45.298855° N, 13.927823° E) and Gabrijelići (GAB, 45.288864° N, 13.959391° E). Samples were taken approximately every 0.5–1.5 m and were analysed for geochemistry and palaeontology, except for Gabrijelići, where only two samples were taken for palaeontological analyses from 10 m of uniform marly sediments, and at Racani, where samples were taken every 25 cm for isotope analysis. In total, 19 samples were collected for foraminifera, 12 for calcareous nannoplankton, 7 for isotopes, and 2 for bulk rock chemistry.
The quality and morphology of the outcrops (limited vertical and lateral extent and vegetation, covering as seen in the Jakomići sections) or monotonous (homogeneous) sedimentological characteristics in the Gabrijelići section contributed to sampling methods that were carried out as part of a preliminary investigation of the oldest of the flysch sequences. Therefore, the analysis result only serves to form a more comprehensive picture of the basin’s history.

2.1. Geochemistry

Bulk rock chemical data were obtained using X-ray fluorescence and inductively couple plasma atomic emission spectroscopy/mass spectrometry at Bureau Veritas Laboratories, Vancouver, BC, Canada. Given that the primary objectives of this study were to infer environmental conditions throughout the water column, as well as potential climatic and terrestrial influences, only samples from two sections (Racani and Jakomići I) were analysed, where preliminary microfossil data were detected for potential warming events. Selected elemental ratios [41] were determined, including traditional aluminium–silica (aluminium oxide [Al2O3], titanium dioxide [TiO2], Fe) trace metals, evidence of a detrital lithogenic origin and/or productivity (barium [Ba]), carbonates (strontium [Sr]) and the diagenetic alteration (Mn). The relative standard deviation for the major elements was 0.01%, whereas for the trace elements, it was within a range of 0.01–8 ppm. The reliability of the results was verified using standards and duplicate sample analysis per session. A LECO C analyser was used to remove the inorganic carbonate minerals and to measure the total C (TOT/C) by combusting the organic C and measuring the resulting carbon dioxide (CO2) and total sulphur (TOT/S) produced in the same laboratory. Furthermore, the determination of total organic carbon (TOC) and nitrogen (N) were carried out in carbonate-free sediment samples treated with 4 mL of hydrochloric acid [42] at the Croatian Geological Survey, Zagreb. Portions of each sample (45–50 mg) were weighed in small tin capsules and analysed in a CN Thermo Scientific FLASH 2000 Organic elemental analyser. The calibration was verified by measuring certified Soil Reference Material NC (Thermo Scientific samples Bremen, Germany), treated in the same way as the carbonate-free samples. Inorganic carbon (TIC) is calculated as the difference between total sediment carbon and TOC. The calcium carbonate (CaCO3) content was determined using calcimetry at the University of Zagreb expressed in weight percent (wt%).
Seven bulk sediment samples were analysed for their oxygen (δ18O) and carbon (δ13C) isotope signatures at the Bloomsbury Environmental Isotope Facility (BEIF) in the Department of Earth Sciences, University College London (UCL), on a Nu Perspective mass spectrometer attached to a Nu Carb preparation device. Standard and bulk sample material (equivalent to 100 ± 20 µg of carbonate) were weighed into individuals. The vials were loaded into the Nu Carb analyser in which each vial was, in turn, evacuated and acidified at 60 °C. The gas released from the samples was then trapped and purified via a series of cryo-traps before being introduced into the dual-inlet system, where it was measured against a reference gas.
The precision of all internal (BDH, NCM) and external National Bureau of standards (NBS19, NBS18) was better than ±0.04 for δ13C and ±0.08 for δ18O. All values are reported as permille using the Vienna Pee Dee Belemnite notation (VPDB) relative to NBS19.

2.2. Palaeontology

2.2.1. Calcareous Nannofossil Analyses

The calcareous nannofossil standard preparation method from the Croatian Geological Survey [43] was used, augmented by the method in [44] for the organic-rich sediments. Approximately 1 cm3 of the sediment was placed in a beaker and treated with H2O2 (30%) to dissolve organic matter; then, it was washed 2–3 times with plain water for the preliminary slide view. Afterwards, further ultrasonication (Bandelin Sonorex Super RK106 bath) was applied for 15 s to improve disaggregation before slide preparation. For the slide preparation, Naphrax (1.74 index), Brunel Microscopes Ltd., Chippenham, UK, was used instead of Norland Optical Adhesive 74 (1.52 index) for better observation in the Leitz Orthoplan polarising light microscope (Ernst Leitz Wetzlar GmbH, Wetzlar, West Germany) in the Department of Geology (University of Zagreb). The nannofossils were observed at 1250× magnification. The preservation of the nannofossils was generally good, albeit slightly affected by dissolution and overgrowth, which did not interfere with their identification. In some cases, larger specimens were partially fragmented in abundant and diverse assemblages. The composition and diversity of the calcareous nannofossil assemblages are presented using the counting method for marginal seas with a 99.8% confidence level [45,46,47]. More than 300 specimens were counted in ½ transect, and the relative abundances of the taxa were classed as scattered (<5%), rare (5–9%), low abundant (10–15%), abundant (16–35%), high abundant (36–50%) and dominant (>50%). In our discussion section, the dominance in assemblage is also expressed as a dominant species with the highest abundance, and a subdominant species is defined as the species with the second highest abundance in assemblage after the dominant species. Rare and scattered species were excluded from paleoceanographic interpretation. To define the stratigraphic position of sections, the standard nannoplankton zones (NP) described in [48] with the regional subzones (MNP) described in [15] were adopted. All the samples are part of the micropalaeontological collections of the Geological Survey of Austria (Vienna) and Croatia (Zagreb).

2.2.2. Foraminiferal Analyses

Out of the 19 samples collected from the Racani, Gabrijelići, and Jakomići sections, only 13 samples were sufficient planktonic foraminifera for obtaining biostratigraphic and palaeoecological interpretation. The remaining six samples were barren in fossils. The samples from Racani and Jakomići were processed using standard methods [49,50], which involved disaggregating the indurated marlstones with 30% hydrogen peroxide. All samples were washed through sieves with mesh sizes ranging from 1000 to 63 µm, and the residues were dried at 40 °C. The 125–250 µm fraction was examined in order to characterise the assemblages and identify the biostratigraphic marker species based on the taxonomic criteria in [51] and using the planktonic foraminiferal standard zonation scheme in [52]. Since the zonation scheme [52] does not account for regional variations in the first appearance of marker species in the Mediterranean region (with strong seasonality and specific hydrography), we were unable to estimate the absolute ages of the identified biozones in our study. Therefore, we followed the approach used in [36] for sediments from the Contessa Highway section. Given the similar paleogeographic settings of both our and Jovane et al.’s research, we correlated our planktonic foraminifera E-zones with the zones defined in [53] and adopted their age estimates for our biozones. This approach was also influenced by studies on the composition of recent planktonic foraminifera in the Mediterranean Sea [54]. These studies demonstrated that the timing of planktonic species first appearances differs from that observed in the open ocean with respect to marginal seas due to the influence of various parameters (i.e., temperature, productivity, nutrient supply).
Relative abundances (expressed as percentages) of the genera and/or species were counted based on ~300 specimens from representative splits of washed residue (the samples were split sufficient times to obtain a fraction with such a number of specimens). Based on these occurrences, the taxa’s relative abundances are also expressed as common = C (˃25%), few = F (6–24%) and rare = R (<5%) according to [55]. Preservation was assessed by applying the criteria from [56], with very good specimens that were glassy under a light microscope with no infilling, good specimens that were semi-translucent with no infilling, moderate recrystallized specimens with opaque test walls, and very poor fragmented, opaque, and infilled specimens. One sample from the Gabrijelići section was analysed for its planktonic foraminifera content, using all fractions greater than 63 µm. Nine species were identified, and the abundances of each taxon were visually estimated as numerous (N) or present (P). Relative abundances and ecological requirements (including deep dwellers, subsurface dwellers, and surface dwellers) for the planktonic foraminifera are provided in Supplement Tables S1 and S2. The ratio of oligotrophic warm indices (mainly Globigerinatheka and Acarinina) and eutrophic cold indices (mainly Subbotina and Turborotalia) for planktonic foraminifera abundances was calculated to assess their response to nutrient temperature changes within the basin (according to [21,23,51] and references therein). Because the planktonic foraminiferal tests were recrystallised, they were not suitable for stable isotope analysis. Our rough estimates indicate that benthic foraminifera constitute a minor proportion of the total assemblages. Therefore, their presence was recorded relative to planktonic foraminifera by counting the number of specimens in aliquots without genetic or ecological classification.

3. Results

3.1. Geochemistry

The highest CaCO3 contents were observed in the Racani (61.86%) and Jakomići I (55.41%) sections. According to the classification in [57], these are marls. The bulk sediment wt % values of Al2O3 and TiO2 for the Racani and Jakomići I sections are 7.01 and 0.34 and 7.99 and 0.40, respectively. The TOT/C and TOT/S contents of the marls are presented in Table 1, along with their different geochemical parameters, of which a detailed discussion is presented in [58]. TOC in the studied samples ranges from 0.11 to 0.13. The low TOC values may indicate low primary productivity, poor organic matter preservation due to an oxygen-rich environment, or a low sedimentation rate. The siliciclastic fraction of the studied marls is rich in clay.
The bulk sediment δ18O values varied between −0.97 and −1.49 for the Racani section and between −1.07 and −1.81 for the Jakomići section, with average values of −1.30 for Racani and −1.41 for Jakomići. The δ18O values showed a slight and gradual increase from the base of the studied interval at Jakomići and a gradual decrease from the base of the studied interval in the Racani section. The absolute temperature estimates derived from the bulk δ18O srecord of both successions are difficult to justify. Bulk sediment δ18O records must be used with caution as a proxy for temperature because they represent mixtures of different components that fractionate δ18O differently and because diagenetic changes further affect the original isotopic signal. The δ13C values from the Jakomići section varied from 0.59 to 1.17, whereas they varied only slightly in the Racani section (from 0.62 to 0.74). The low positive values can be attributed to environmental (higher temperature, greater CO2 availability), biological (productivity,) or environmental (redox state processes). The bulk δ13C and δ18O values corresponded to values (0 ± 4‰ VPDB for δ13C and 0 ± 8‰ VPDB δ18O) indicative of primary biogenic carbonates [59].

3.2. Palaeontology

3.2.1. Calcareous Nannofossils

In total, 130 coccolith taxa were identified using the method in [45] with the amended names from the Nannotax website; seeable (https://www.mikrotax.org/Nannotax3; accessed on 26 June 2025), Supplement List S1 (https://urn.nsk.hr/urn:nbn:hr:217:467647; created 7 June 2023). The distributions of the species relevant for palaeoecology and biostratigraphy are shown in Figure 2, while light microscope images of nannofossil species at the Racani and Jakomići sections are shown in Figure 3.
The most abundant species in the assemblages were Cyclicargolithus floridanus (up to 52% in RAC) and Reticulofenestra minuta (43% in GAB), followed by abundant R. producta (up to 25% in JAK), Zygrhablithus bijugatus (up to 22% in RAC), R. bisecta (up to 21% in J) and Coccolithus pelagicus (up to 20% in RAC). Less abundant was Coccolithus formosus (up to 12% in RAC). The most diverse assemblages were found in the Racani section (73), followed by Jakomići I (71) and II (65) and Gabrijelići (38). Based on the frequency of occurrence, C. formosus, C. pelagicus, C. floridanus, Discoaster barbadiensis, D. deflandrei, Helicosphaera bramlettei, Reticulofenestra dictyoda, R. minuta, Sphenolithus furcatolithoides, S. radians, S. spiniger and Z. bijugatus were identified in >90% of the samples (exactly in 11/12 samples). The percentage of reworked older species from the Cretaceous to Mid-Eocene in the assemblages is very small (RAC < 2.6%, J < 2.2%, JAK < 3.9% and GAB ~5%). Thus, they did not influence our interpretations.
The top occurrence (T) of Nannotetrina spp. (N. cristata) observed in sample RAC 2b and the base regular (Br) occurrence of R. umbilicus in sample RAC 2a indicate Lutetian Zone NP16 [48] and the base of Subzone MNP16A, set 42.25 Ma [15,36] (Figure 2). The T Sphenolithus furcatolithoides, determined in sample GAB 2, marking the top of Subzon MNP16A in the Mediterranean at 40.51 Ma [15,36], which coincides with the Br occurrence of R. bisecta, also noticed in our section (Figure 2). The base (B) of Furcatolithus obtusus, noticed at the top of the Jakomići I section (sample J3; Figure 2), defines the MNP16B/MNP17A boundary. It occurs in the same sample together with T of Sphenolithus spiniger, a secondary marker, as in nearby Alano section in Italy, dated at 39.63 Ma, i.e., 39.8 Ma in the North Atlantic Site 1052 [15] (Figure 1, Figure 2 and Figure 4). The B of Furcatolithus obtusus, noticed at the base of the Jakomići II section (sample JAK 1; Figure 2), defines the base of MNP17A. The T Sphenolithus spiniger in the next sample (JAK 3) confirms the subzone.

3.2.2. Foraminifera

The Racani samples contained abundant and moderately diverse assemblages of planktonic foraminifera, with a total of 32 species and nine genera (Supplementary Tables S1 and S2). The assemblages are characteristic of subtropical pelagic settings, represented by common and abundant Subbotina, common Turborotalia, Acarinina, and Pseudohastigerina, rare Globigerinatheka and Hantkenina, and sporadic and very rare Igorina, Morozovelloides, and Globorotaloides. Three genera had the highest species diversity (six to seven species of Acarinina, Globigerinatheka, and Subbotina). Two species—Acarinina topilensis and Hantkenina liebusi—occur only in one sample.
The planktonic foraminifera assemblage from the Gabrijelići section displayed moderate diversity. Among the nine species identified, Subbotina species are the most abundant, Turborotalia less, and there are only rare occurrences of Globigerinatheka and muricate Morozovelloides.
Sixteen species and seven genera of planktonic foraminifera were determined in the Jakomići I section. The common and abundant genera are Subbotina (with five species) and Turborotalia (with four species). Acarinina and Globigerinatheka were less abundant, while the rare genera Globoanomalina, Paragloborotalia, and Tenuitella are rare and only occurred in this section. The planktonic foraminifera assemblages of the Jakomići II section are characterised by four common and abundant genera—Subbotina and Turborotalia (each with four species) and Globigerinatheka and Acarinina (each with three species). A rare occurrence of Dentoglobigerina was recorded only in this section. In total, there are 15 species and 5 genera in this section.
The test preservation was moderate/recrystallised in all the samples. Diagenetic alterations included filling the chamber lumens (internal moulds), apertures obscured by sediment, and changes to the original wall texture. Generally, test fragmentation was low in all the samples.

4. Discussion

4.1. The LLTM/C19r Event

4.1.1. Bioevents

Globally, the event occurred in Chron C19r, as recorded in the equatorial North Atlantic between 42.196 and 41.18 Ma (GTS20). Close to the base of C19r is the base common occurrence (Bc) of the nannofossil Reticulofenestra reticulata, estimated at 42.37 Ma [60] in the North Atlantic (Figure 5). Regionally, in the Betic Cordillera, Spain, a study Ref. [13] used Br of R. reticulata as a marker for the base of C19r. This occurred in an assemblage with the Br of R. umbilicus and the T of Nannotetrina spp. The Br of R. umbilicus, together with the Br of R. reticulata and the T of Nannotetrina spp. in Italy has been determined to be 42.25 Ma in the Bottaccione and Contessa sections [15,36], close to the base of Chron C19r according to [33] (Figure 4). The Br of R. reticulata and the Br of R. umbilicus have been identified in central eastern Neotethys as well [23].
The T of Nannotetrina spp. in the Racani section and the Br of R. umbilicus point to Zone NP16 [48] and Lutetian Subzone MNP16A [15,36] (Figure 2 and Figure 3(4–5,27)). Due to the absence of an index species for foraminifera, also noted in previous regional studies [37,65], biostratigraphic attribution in the studied samples was based on the overlapping stratigraphic ranges of the identified species. The presence of the planktonic foraminifera Turborotalia pomeroli, along with other species such as A. rohri and Morovovelloides crassatus in the organic-rich dark layer (RAC 3) as well as differences in assemblage composition compared to the overlying layers (Supplement Tables S1 and S2, Figure 4 and Figure 5), indicated that the upper part of the Racani section can be assigned to the Morozovelloides lehneri partial range zone (PRZ), equivalent to E11 [51,66]. Therefore, planktonic foraminiferal association below the organic-rich layer corresponded to either uppermost E10 (Acarinina praetopilensis PRZ) or, more probably, E11 in [51,64] (Figure 4 and Figure 5). This interpretation was based on the presence of Globigerinatheka subconglobata, Subbotina linaperta, S. eocaena, and A. praetopilensis (Supplement Tables S1 and S2). The E10–E11 interval was characterised by common abundances of turborotalids (Turborotalia frontosa) and some acarininids (A. praetopilensis), with rare abundances of A. mcgowrani and A. topilensis, subbotinids comprising more than 26.80% of the total assemblage (the most common species being S. eocaena and S. linaperta) and rare occurrences of globigerinathekas (G. index, G. barri, G. eugenea).

4.1.2. Response of Calcareous Plankton to Hyperthermal Event Indicators

The E10/E11 boundary (41.89 Ma) in the organic-rich marly interval coincided with the high insolation peak in the Northern Hemisphere, set to 41.913 Ma in [7]. It is well known that the Earth’s atmospheric CO2 thermal maximum was accompanied by major negative δ13C excursions [67]. The maximum negative δ13C in the Southern Hemisphere was set to 41.8 Ma (Figure 4) but with no interpretation of the LLTM in [18] and there were no included records below 41.56 Ma in [9]. Organic-rich dark shales and clay layers characterise these negative δ13C excursions both globally (the dark clay-rich layer in [9] and regionally (the dark clay layer in [33]), which is also observed in the Racani section (Figure 4). Close to the peak climatic condition, there was a rapid deposition of organic-rich sediments, with marls below that contain 0.11% TOC concentrations (Table 1, Figure 4), associated with the TOT/S (0.29%) and low concentrations of Mn (0.12%), implying low, possibly dysoxic, bottom water conditions [68]. Manganese precipitates as oxyhydroxides in the Eh and pH ranges characteristic of well-oxygenated seawater [68]. The carbonate concentration is unusually high (61.86%) for north latitudes but can be correlated with South Atlantic Site 1263 (83%) during the event.
A trend of somewhat lower abundances of smaller benthic foraminifera can be seen in the Istrian Basin [37,65], with most of the samples containing between 0.7 and 3%, except for samples JAK1 and JAK 3, which reach 3.88% and 5.34%, and sample J3, which shows a notable increase to nearly 15%. This pattern suggests that, during the middle Lutetian environmental disturbances, perhaps there were variations in the types of organic material being transported to the seafloor. This fits with a period in the middle Eocene when there was a turnover of small benthic foraminifera [69] and references therein. The composition of the planktonic foraminiferal assemblages (predominantly deep-dwelling Subbotina and common subsurface-dwelling Turborotalia) and the lower proportions (up to 20%) of small benthic foraminifera (Supplement Tables S1 and S2) indicate mesotrophic-to- eutrophic conditions in the lower bathyal zone [70,71]. Also, the common abundance of the opportunistic species Pseudohastigerina micra (up to 26.10%) in some samples indicates a more stressful eutrophic environment [21,72]. The warm index planktonic foraminifera Acarinina shows low abundances in the lower part of the Racani section, but it increases in the middle part (reaching up to 27.5%; Supplement Table S1), as would be expected in the LLTM warm period. The abundances of the opportunistic subbotinid and turborotalids before and after the LLTM resulted from the eutrophic conditions in their habitats that arose from a combination of geographical location (hydrography) and the circulation pattern in the surface mixed layer [73]. It can also be related to the lower temperatures with respect to the event, as these genera are also considered cold indicators. The relative common finding of deep-water thermocline subbotinids is consistent with the presumption that specimens can ascend to higher habitats in the water column [26,74].
The warm-water oligotrophic C. floridanus [75] dominates (up to 52%) in the nannofossil assemblages (Figure 2 and Figure 3(14)), pointing to a more mesotrophic status in the photic zone (ref. [23,76], which is in accordance with a major change in coccolithophore assemblage compositions during the LLTM together with decreased abundances of subdominant warm-water oligotrophic Z. bijugatus [11,77] from up to 22% before the LLTM to 9% prior to theCIE peak (Figure 2). It seems that C. floridanus characterises the initial CIE phase, because [23] also encountered this, but prior to the MECO CIE peak in the central eastern Neotethys, a similar situation—the —domination of C. floridanus—suggests increased mesotrophic conditions. Its dominance in the anoxic level in the LLTM (41.6 Ma) in Spain [35] was similar to our assemblages. This unstable, possibly stratified environment had periodic nutrient inputs from upwelling, which induced eutrophication (indicated by 20% larger C. pelagicus) [78,79,80]. The indication of climate seasonality (seasonal rainfall) under dry conditions is evident in the presence of smectite-interlayered phases and occasional spikes in kaolinite content [58,81]. This coincided with the increased productivity during the high insolation peak at 41.9 Ma, which promoted the negative δ13C excursion (0.62‰), suggesting that the earliest record of the LLTM CIE occurred earlier in the north in the Neotethys, as detected previously in the Contessa section (δ13C ~0.9‰ at 41.54 Ma) as in Spain, than in the Southern Hemisphere (δ13C = 1.7‰ at 41.52 Ma), with the latest record in the Tasman Sea set to 41.39 Ma [82]. In addition, the highest nannofossil species richness [83] supported the high productivity noted globally during the CIE [9], although this is not always the case [84]. The higher maximum CIE here could also be a consequence of the more marginal environment of the Neotethys (Figure 1).

4.2. The MECO Event

The MECO is a complex global warming event [84]. Reference [23] divided the MECO event into several phases in the Neotethys. Here, the pre-MECO, CIE (interval) and post-MECO phases have been encountered.

4.2.1. Bioevents

The pre-MECO phase occurred at ~40.51 Ma in the Neothethys [16]. It was characterised by the T of Sphenolithus furcatolithoides (dated at 40.51 Ma in the northern -midlatitudes), marking the top MNP16A in the Mediterranean [61,85] after GTS12 [15,36]. It occurred at the same time in the northern North Atlantic (40.51 Ma) in Chron C18r [60]. In the lowerlatitude North Atlantic, it seems to have occurred later (40.384 Ma) in NP16 but close to the NP16/NP17 boundary (40.4 Ma), based on the T of Chiasmolithus solitus (Figure 4), although this is not a reliable marker at all latitudes [15] and, as such, is not generally used [86]. According to [33], the B (i.e., the Bc) of R. bisecta lies in Chron C18n2n, close to the CIE interval in the MECO, whose base (i.e., the Br) of the South Atlantic was dated to 40.32 Ma, i.e., 40.08 Ma in [3] and [16]. In the North Atlantic, it occurs at 40.354 Ma [60], which is consistent with Chron C18r2r (Figure 4) as its base in the central eastern Neotethys (40.6 Ma; [87]). In the central western Neotethys, the Bc (i.e., Br) of R. bisecta occurred at 40.59–40.373 Ma (Figure 4), but all were within C18r2r [15]. Reference [36] astronomically calibrated the Bc of R. bisecta to 39.86 Ma (Chron C17; GTS12) in Contessa, which does not support the aforementioned global and regional records. Recent calibrations [61] in Alano put its base to the top of Chron C18r. For this reason, we ignore Contessa correlations with GTS here but give its calibrated age in Figure 4, which is in agreement with Chron C18n2n as in the South Hemisphere.
Our data confirms the aforementioned occurrences within Chron C18r in the lower latitude of the North and South Atlantic (Figure 2 and Figure 4) and are close to the nearby Alano. A widespread, relatively reliable marker is the B (Bc) of Furcatolithus obtusus, which has been dated in North Atlantic International Ocean Discovery Program Site 1052 at 40.127 Ma along with the CIE in Chron C18n2n [33], as well as in North Atlantic IODP Site 1051 at 40.08 Ma [18], pointing to Chron boundary C18r/C18n (40.073 Ma; GTS20), together with the Tc of Sphenolithus spiniger [60] (Figure 4). This event occurs at the top of the Jakomići section (Figure 2 and Figure 4), together with the T of Sphenolithus spiniger, albeit being a little later in the Mediterranean (39.633 Ma; [15] (Figure 3(1–4,5)) pointing regionally to Chron boundary C18n.2n/C18n.1r (ref. [61] (Figure 4). Based on differences in the occurrences and (rare to few) abundances of certain planktonic foraminifera (S. hagni, Dentoglobigerina galavisi, Paragloborotalia nana, Tenuitella sp.) the Jakomići sediments were interpreted as slightly younger than the other sections but still within E11 (Supplement Tables S1 and S2, Figure 5).

4.2.2. Calcareous Plankton Response to Warming Event

The T of S. furcatolithoides correlated with the most prominent δ13C value (˂1‰) at 45° N and ˂2‰ in the Northern Hemisphere, while in the South, it was >2‰ (Figure 3). These suggest increased productivity under higher temperatures that occurred in the northern mid-slatitude. The T of S. furcatolithoides in the Gabrijelići section occurred together with common occurrences of reticulofenestrids and sphenoliths, which is similar to the Mediterranean records in [15,16] during the pre-MECO phase. Small placoliths (R. minuta 43% and R. producta 16%) dominate the assemblage (Figure 2 and Figure 3(9,15)), suggesting possibly shallow and stratified -warmwater environments with highly fluctuating salinity and nutrient levels during periods of runoff [79,88]. The clay composition indicates the dominant influence of physical weathering, characterised by a considerable amount of illite and chlorite [57]. Episodes of enhanced continental weathering have also been documented in the Tunisian Dorsal across the Lutetian/Bartonian transition, as well as in Istria, whereas in central Tunisia, Italy (Alano, Bottaccione, and Spettine sections,) and Turkey, there is a hiatus at the boundary [16], as well as in the South Atlantic at Site 1263 [15]. Shallowing and runoff, which induced eutrophication, could have influenced the decreased abundances of discoasters (1.4%) during the pre-MECO phase in Istria compared with deep-sea sites.
The CIE phase of the MECO (with a peak at ~40.08 Ma) has been linked to a transient increase in atmospheric greenhouse gas (pCO2), which induced deep-water acidification and a sharp decrease in carbonate accumulation [18]. The concentration of TOC was slightly higher (0.13%) in the laminated marls at the base of the Jakomići section (at 39.63 Ma) than in the LLTM in the Racani section (Table 1), thus providing a good second peak CIE correlation (Figure 4) with the enhanced carbonate dissolution interval characteristic of warming (Table 1). This second peak is actually higher (0.59‰) than the global MECO CIE value (~1.5‰), also recorded in Contessa and Alano (Figure 4), prolonging the MECO phase in the Northern Hemisphere. This event indicates Subzone MNP16Bc in the interval that coincides with another δ13C peak (negative δ13C excursion of ~1‰ at 45° N) at ~39.8 Ma in the Northern Hemisphere [15,18]; herein, Figure 4. Reticulofenestra bisecta dominated (up to 21%) in the assemblage (Figure 2) with the highest species richness (71) (similar to the 73 species in the LLTM, Supplement List S1, https://urn.nsk.hr/urn:nbn:hr:217:467647; created 7 June 2023), indicating warm and productive waters under enhanced eutrophic conditions, which agrees with the conditions during the warming peak in the Neotethys [16,23] and globally [9]. The higher abundances of Turborotalia spp. in the Jakomići sections (Supplementary Tables S1 and S2) followed the trend observed in the Racani section, where turborotaliids prevailed after the LLTM, in contrast to the dominance of Subbotina spp. before the event. Abundant cold-water planktonic foraminifera species have been recorded in the western and eastern parts of the Neotethys [21,23,25,26], confirming their opportunistic way of life and proliferation under enhanced eutrophic conditions. The species benefited from a high nutrient input to the thermocline zone. This rare occurrence, or even absence, of the warm-water dwelling genera seems to be a Neotethyan characteristic, as recorded in Ligurian sections [25,26].
The post-MECO phase was characterised by an abrupt decrease in temperatures over 50 kyr after the global peak warming, although in the North Atlantic, this warming lasted until 39.3 Ma [18] (Figure 4 and Figure 5). The warm conditions prevailed, with fluctuating nutrient and productivity levels similar to the pre-MECO phase in the Neotethys [23]. These conditions were recorded in the Jakomići II section in MNP17A, based on the B of F. obtusus (Figure 2 and Figure 4). Reticulofenestra producta increased (up to 25%) in the assemblages (Figure 2 and Figure 3(15)), suggesting a shallower and more mesotrophic environment [84]. The species richness (65) decreased, probably due to the initiation of the general (post-MECO) cooling phase, which induced eutrophication (indicated by up to 11% smaller C. pelagicus [78,89]). The post-MECO stage in the relatively shallow Istrian Basin was characterised by the co-occurrence of globigerinathekas and subbotinas. The abundance of globigerinathekas in the Istrian Basin is similar to what has been reported in other parts of the Neotethys [21,22,23]. It appears that the distribution of the globigerinathekas, similarly to the subbotinas, depended much more on the trophic regime than on temperature. This confirms that the carbon isotope signature for the MECO (from the pre- to the post-phase) varies from site to site and is therefore difficult to interpret [84].
All our sections were deposited in hemipelagic settings (Figure 1) within a relatively narrow, restricted, and shallow-water basin [37]. The low-to- moderate species diversity and the dominance of thermocline living planktonic foraminifera species suggest unstable surface conditions or conditions unfavourable for planktonic foraminifera in the mixed layer (low abundance or even absence of surface-dwelling species, Supplement Table S1). More favourable conditions for the eutrophic taxa prevailed deeper in the water column. This could be due to the proximity of the mainland (Cretaceous sediments in the southwest of the basin and the evolving Dinaric Orogen in the northeast) (Figure 1) and the higher terrigenous fluxes (indicated by increased Fe, Ti, and Al) during sedimentation (Supplement Table S2). These palaeogeographical conditions could have resulted in a high nutrient input, favouring high abundances of primary producers. In addition, the confined Istrian Basin could also have experience relatively low salinity and high turbidity. These conditions were not favourable for the specialised planktonic foraminifera living in the mixed layer [90], and this might have caused their lower abundances in our sections. The dominance of Subbotina species around both warm episodes suggest their ability to benefit from increased nutrient supply associated with an enhanced hydrological cycle. Additionally, the decline in oligotrophic mixed-layer-dwelling planktonic foraminifera may have been caused by the possible input of fresh surface waters that may have become slightly acid [86] or have reduced salinity, conditions under which planktonic foraminifera are not specialised for. All these point to a stratified water column but raise questions about the stability and expansion of the mixed layer during the LLTM and MECO.

5. Conclusions

Four sections of Eocene (Lutetian–Bartonian) hemipelagic sediments from the Istrian Basin (Outer Dinarides, Adriatic Sea) of the central Neotethys were studied to determine the environmental and biotic changes that occurred during two warming events, namely the Late Lutetian Thermal Maximum and the Middle Eocene Climate Optimum. We analysed the calcareous nannofossils, planktonic foraminifera, bulk-sediment δ13C isotope, and geochemical composition of the selected samples. Our data indicate the complexity of both warming events, from the triggering parameters that caused them to the timing at both regional and global scales. Both events resulted in warm and productive waters, eutrophic conditions with a deeper mixed layer, and weaker stratification, suggesting compressed depth habitats.
The nannofossil bioevents we determined correlated better with thermal events based on regional subzones than with the global zones used in the Neotethys. This was also the case with the planktonic foraminifera E10/E11 boundary (41.89 Ma), which also coincided with the highest insolation peak in the Northern Hemisphere (at 41.913 Ma), whereas in the Southern Hemisphere, this occurred 0.4 Myr later (41.5 Ma). In general, the most frequent nannofossil taxa in the sections indicate warm marine environments with nutrient and depth fluctuations during the mid-Eocene warming events. These conditions influenced species diversity and productivity. The highest species richness values were in the LLTM and MECO-CIE warming phases in the region and were broader, albeit with slight discrepancies in the timing.
Our data seems to confirm that the LLTM occurred earlier in the Northern Hemisphere, suggesting different impacts at global and regional scales. The event corresponds in our setting to the deposition of organic-rich dark marls with positive low δ13C values and the occurrence of smectite layers formed under the condition of seasonal rainfalls and a humid and warm climate that coincided ecologically and geochemically with the dark and organic-rich layers that followed the peak warming. These conditions result from the increasing eutrophication in the marginal seas caused by periodic changes in circulation and possible upwelling.
The MECO event was recorded as pre-, CIE (interval,) and post-MECO phases. The carbon signature values differ from sites around the world, confirming its peculiarity. The changes in water circulation began with fluctuating salinity and nutrient levels during periods of pronounced runoff. The pre-MECO phase was influenced by the wetter subtropical climate in the region. Warm and productive waters under enhanced eutrophic conditions characterised the MECO and the LLTM, with the deep thermocline hosting cool-water foraminifera.
The warm condition prevailed in the post-MECO environment, with the fluctuating nutrient (oligotrophic–eutrophic) and productivity levels being similar to the pre-MECO phase in the Neotethys.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/geosciences15090366/s1. Supplement Table S1. List of planktonic foraminifera species found in the Racani (RAC), Gabrijelići (GAB), Jakomići I (J) and Jakomići II (JAK) sections, with their relative abundances in the samples expressed as percentages and their ecological preferences (according to [21,23,29] and references therein). Supplement Table S2. List of planktonic foraminifera species found in the Racani (RAC), Gabrijelići (GAB), Jakomići I (J) and Jakomići II (JAK) sections, with their relative abundances in the samples expressed as common = C (>25%), few = F (6–24%) and rare = R (<5%) according to [54]. Supplement List S1. The calcareous nannofossils determined in assemblages during the LLTM and MECO events.

Author Contributions

Conceptualization, I.G. and Đ.P.; methodology, I.G., V.Ć. and M.H.; validation, I.G., R.L., K.M., Đ.P., M.H. and V.Ć.; formal analyses, K.M. and R.L.; data curation, K.P.; writing—original draft preparation, I.G., Đ.P., M.H. and V.Ć.; writing, review and editing, I.G. and Đ.P.; visualisation, K.P.; supervision, funding acquisition, and bearer of the issue, V.Ć. Same contribution as the first author, Đ.P. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Croatian Science Foundation (BREEMECO Project IP-2019-04-5775) https://projectbremeeco.wordpress.com/, accessed on 21 August 2025. Additional analyses (TOC, TIC, N) and English editing were conducted in the scope of the internal research project “ZG-LAB” at the Croatian Geological Survey, funded by the National Recovery and Resilience Plan 2021–2026 of the European Union—NextGenerationEU and monitored by the Ministry of Science, Education and Youth of the Republic of Croatia.

Data Availability Statement

The entire datasets are archived at the Repository of the Faculty of Science, University of Zagreb (https://repozitorij.pmf.unizg.hr/en/islandora/object/pmf%3A11719, accessed on 21 August 2025). The calcareous nannofossil slides are available at the Geological Survey of Austria and the Croatian Geological Survey (contact ingalovic@hgi-cgs.hr), while the foraminifera are available at the University of Zagreb, with all raw samples stored at the University of Zagreb (vcosovic@geol.pmf.hr). Figure 1: Geological map M:300000 with base map at https://maps-for-free.com, accessed on 21 August 2025. Figure 2: Free C2 meprogram for environmental and palaeontological data presentation was used (https://www.staff.ncl.ac.uk/stephen.juggins/software/C2Home.htm, accessed on 21 August 2025) (Juggins, 2007) [91]. Figure 3: Adobe Illustrator CS6 at the Croatian Geological Survey available under the Adobe license at https://www.adobe.com/products/illustrator.html, accessed on 21 August 2025. Figure 4: Corel 11 (at the Croatian Geological Survey, available under the CorelDraw license at https://www.coreldraw.com/en/, accessed on 21 August 2025). Data are contained within the article and Supplementary Material.

Acknowledgments

We thank Dragica Kovačić (Croatian Geological Survey) for the laboratory assistance; Martina Šparica Miko for the TOC, TIC, andN analyses (Croatian Geological Survey), Rober Košćal (Faculty of Science, Croatia) for his help with drawing the sections; Mirjana Miknić (Croatian Geological Survey) for providing the Gabrijelići foraminifera data; and Stjepan Ćorić (Geosphere, Vienna) for the Racani nannofossil data. We are also grateful to Anne-Lise Jourdan at the BEIF (UCL) for providing us with the isotope data.

Conflicts of Interest

The authors declare no conflicts of interest.

References

  1. Boscolo Galazzo, F.; Thomas, E.; Pagani, M.; Warren, C.; Luciani, V.; Giusberti, L. The Middle Eocene Climatic Optimum (MECO): A multiproxy record of paleoceanographic changes in the Southeast Atlantic (ODP Site 1263, Walvis Ridge). Paleoceanography 2014, 29, 1143–1161. [Google Scholar] [CrossRef]
  2. Arimoto, J.; Nishi, H.; Kuroyanagi, A.; Takashima, R.; Matsui, H.; Ikehara, M. Changes in upper ocean hydrography and productivity across the Middle Eocene Climate Optimum: Local insights and global implications from the Northwest Atlantic. Glob. Planet. Change 2020, 193, 103258. [Google Scholar] [CrossRef]
  3. Westerhold, T.; Marwan, N.; Drury, A.J.; Liebrand, D.; Agnini, C.; Anagnostou, A.; Barnet, J.S.K.; Bohaty, S.M.; de Vleeschouwer, D.; Florindo, F.; et al. An astronomically dated record of Earth’s climate and its predictability over the last 66 million years. Science 2020, 369, 1383–1387. [Google Scholar] [CrossRef] [PubMed]
  4. van der Ploeg, R.; Cramwinckel, M.J.; Kocken, I.J.; Leutert, T.J.; Bohaty, S.M.; Fokkema, C.D.; Hull, P.M.; Meckler, A.N.; Middleburg, J.J.; Muller, I.A.; et al. North Atlantic surface warming and salinization in response to middle Eocene greenhouse warming. Sci. Adv. 2023, 9, eabq0110. [Google Scholar] [CrossRef] [PubMed]
  5. Laskar, J.; Robutel, P.; Joutel, F.; Gastineau, M.; Correia, A.; Levrard, B. A long-term numerical solution for the insolation quantities of the Earth. Astron. Astrophys. 2004, 428, 261–285. [Google Scholar] [CrossRef]
  6. Westerhold, T.; Rohl, U. Orbital pacing of Eocene climate during the Middle Eocene Climate Optimum and the Chron C19r event: Missing link found in the tropical western Atlantic. Geochem. Geophys. Geosyst. 2013, 14, 4811–4825. [Google Scholar] [CrossRef]
  7. Westerhold, T.; Röhl, U.; Frederichs, T.; Agnini, C.; Raffi, I.; Zachos, J.C.; Wilkens, R.H. Astronomical calibration of the Ypresian time scale. Pangaea 2017, 13, 1129–1152. [Google Scholar] [CrossRef]
  8. Edgar, K.M.; Wilson, P.A.; Sexton, P.F.; Suganuma, Y. No extreme bipolar glaciation during the main Eocene calcite compensation shift. Nature 2007, 448, 908–911. [Google Scholar] [CrossRef]
  9. Westerhold, T.; Röhl, U.; Donner, B.; Zachos, J.C. Global extent of early Eocene hyperthermal events: A new Pacific benthic foraminiferal isotope record from Shatsky Rise (ODP Site 1209). Paleoceanogr. Paleoclimatol. Paleoecol. 2018, 33, 626–642. [Google Scholar] [CrossRef]
  10. Soták, J.; Elbra, T.; Pruner, P.; Antolíková, S.; Schnobl, P.; Biron, A.; Kdyr, Š.; Milonsky, R. End-Cretaceous to middle Eocene events from the Alpine Tethys: Multi-proxy data from a reference section at Kršteňany (Western Carpathians). Paleogeogr. Paleoclimatol. Paleoecol. 2021, 579, 110571. [Google Scholar] [CrossRef]
  11. Intxauspe-Zubiaurre, B.; Martínez-Braceras, N.; Payros, A.; Ortiz, S.; Dinarès-Turell, J.; Flores, J.-A. The last Eocene hyperthermal (Chron C19r event, ~41.5 Ma): Chronological and paleoenvironmental insights from a continental margin (Cape Oyambre, N Spain). Paleogeogr. Paleoclimatol. Paleoecol. 2018, 505, 198–216. [Google Scholar] [CrossRef]
  12. Rivero-Cuesta, L.; Westerhold, T.; Alegret, L. The Late Lutetian Thermal Maximum (middle Eocene): First record of deep-seabenthic foraminiferal response. Palaeogeogr. Palaeoclimat. Palaeoecol. 2020, 545, 109637. [Google Scholar] [CrossRef]
  13. Tori, F.; Monechi, S. Lutetian calcareous nannofossil events in the Agost section (Spain): Implications toward a revision of the Middle Eocene biomagnetostratigraphy. Lethaia 2013, 46, 293–307. [Google Scholar] [CrossRef]
  14. Bralower, T.J. Data report: Paleocene–early Oligocene calcareous nannofossil biostratigraphy, ODP Leg 198 Sites 1209, 1210, and 1211 (Shatsky Rise, Pacific Ocean). In Proceedings of the Ocean Drilling Program, Scientific Results, College Station, TX, USA, 27 August–23 October 2005; Bralower, T.J., Premoli Silva, I., Malone, M.J., Eds.; Ocean Drilling Program: College Station, TX, USA, 2005; Volume 198, pp. 1–15. [Google Scholar]
  15. Fornaciari, E.; Agnini, C.; Catanzariti, R.; Rio, D.; Bolla, E.M.; Valvasoni, E. Mid-latitude calcareous nannofossil biostratigraphy and biochronology across the middle to late Eocene transition. Stratigraphy 2010, 7, 229–264. [Google Scholar] [CrossRef]
  16. Messaoud, J.H.; Thibault, N.; Bomou, B.; Adatte, T.; Monkenbusch, J.; Spangenberg, J.E.; Aljahdali, H.A.; Yaich, C. Integrated stratigraphy of the middle–upper Eocene Souar Formation (Tunisian Dorsal): Implications for the Middle Eocene Climatic Optimum (MECO) in the SW Neo-Tethys. Paleogeogr. Palaeoclimatol. Paleoecol. 2021, 581, 110639. [Google Scholar] [CrossRef]
  17. Bohaty, S.M.; Zachos, J.C. Significant Southern Ocean warming event in the late middle Eocene. Geology 2003, 31, 1017–1020. [Google Scholar] [CrossRef]
  18. Bohaty, S.M.; Zachos, J.C.; Florindo, F.; Delaney, M.L. Coupled greenhouse warming and deep-sea acidification in the middle Eocene. Paleoceanography 2009, 24, PA2207. [Google Scholar] [CrossRef]
  19. Zhang, L.; Hay, W.W.; Wang, C.; Gu, X. The evolution of latitudinal temperature gradients from the latest Cretaceous through the Present. Earth-Sci. Rev. 2019, 189, 3274. [Google Scholar] [CrossRef]
  20. Cramwinckel, M.J.; Coxall, H.K.; Śliwińska, K.K.; Polling, M.; Harper, D.T.; Bijl, P.K.; Brinkhuis, H.; Eldrett, J.S.; Houben, J.P.; Peterse, F.; et al. A warm, stratified, and restricted Labrador Sea across the middle Eocene and its climatic optimum. Paleoceanogr. Paleoclimatol. 2020, 35, e2020PA003932. [Google Scholar] [CrossRef]
  21. Luciani, V.; Giusberti, L.; Agnini, C.; Fornaciari, E.; Rio, D.; Spofforth, D.J.A.; Palike, H. Ecological and evolutionary response of Tethyan planktonic foraminifera to the Middle Eocene Climate Optimum (MECO) from the Alano section (NE Italy). Palaeogeogr. Palaeoclimatol. Palaeoecol. 2010, 292, 82–95. [Google Scholar] [CrossRef]
  22. van der Boon, A.; van der Ploeg, R.; Cramwinckel, M.J.; Kuiper, K.F.; Popov, S.P.; Tabachnikova, I.P.; Palcu, D.V.; Krijgsman, W. Integrated stratigraphy of the Eocene–Oligocene deposits of the northern Caucasus (Belaya River, Russia): Intermittent oxygen-depleted episodes in the Peri-Tethys and Paratethys. Paleogeogr. Paleoclimatol. Paleoecol. 2019, 536, 109–395. [Google Scholar] [CrossRef]
  23. D’Onofrio, R.; Zaky, A.S.; Frontalini, F.; Luciani, V.; Catanzariti, R.; Francescangeli, F.; Giorgioni, M.; Coccioni, R.; Özcan, E.; Jovane, L. Impact of the Middle Eocene Climatic Optimum (MECO) on foraminiferal and calcareous nannofossil assemblages in the Neo-Tethyan Baskil section (eastern Turkey): Paleoenvironmental and paleoclimatic reconstructions. Appl. Sci. 2021, 11, 11339. [Google Scholar] [CrossRef]
  24. Gandolfi, A.; Giraldo-Gomez, V.M.; Luciani, V.; Piazza, M.; Adatte, T.; Arena, L.; Bomou, B.; Fornaciari, E.; Frija, G.; Kocsis, L.; et al. The Middle Eocene Climatic Optimum (MECO) impact on the benthic and planktonic foraminifera resilience from a shallow-water sedimentary recirs. Riv. Ital. Di Paleontol. Stratigr. 2023, 129, 629–651. [Google Scholar]
  25. Gandolfi, A.; Giraldo-Gómez, V.M.; Luciani, V.; Piazza, M.; Brombin, V.; Crobu, S.; Papazzoni, C.A.; Pignatti, J.; Briguglio, A. Unraveling ecological signals related to the MECO onset through planktic and benthic foraminiferal records along a mixed car-bonate-silciclastic shallow-water succession. Mar. Micropaleontol. 2024, 190, 102388. [Google Scholar] [CrossRef]
  26. Gandolfi, A.; Giraldo-Gómez, V.M.; Arena, L.; Luciani, V.; Papazzoni, C.A.; Pignatti, J.; Piazza, M.; Kocsis, L.; Baumgartner, C.; Briguglio, A. Diverse ecological responses of foraminifera to the Middle Eocene Climatic Optimum (MECO) in shallow-water settings (Provençal Domain, NW Italy). Palaeogeogr. Palaeoclimatol. Palaeoecol. 2025, 661, 112697. [Google Scholar] [CrossRef]
  27. Wade, B.S. Planktonic foraminiferal biostratigraphy and mechanisms in the extinction of Morozovella in the late middle Eocene. Mar. Micropaleontol. 2004, 51, 23–38. [Google Scholar] [CrossRef]
  28. Berggren, W.A.; Olsson, R.K.; Premoli Silva, I. Chapter 1 Taxonomy, biostratigraphy and phylogenetic affinities of Eocene Astrorotalia, Igorina, Planorotalites, and Problematica (Praemurica? lozanoi). In Atlas of Eocene Planktonic Foraminifera; Pearson, P.N., Olsson, R.K., Huber, B.T., Hemleben, C., Berggren, W.A., Eds.; Cushman Foundation for Foraminiferal Research: Fredrickburg, VA, USA, 2006; Volume 41, pp. 377–400. [Google Scholar]
  29. Pearson, P.N.; Berggren, W.A. Chapter 10: Taxonomy, biostratigraphy, and phylogeny of Morozovelloides n. gen. In Atlas of Eocene Planktonic Foraminifera; Pearson, P.N., Olsson, R.K., Huber, B.T., Hemleben, C., Berggren, W.A., Eds.; Cushman Foundation for Foraminiferal Research: Fredrickburg, VA, USA, 2006; Volume 41, pp. 327–341. [Google Scholar]
  30. Fraass, A.J.; Kelly, D.K.; Peters, S. Macroevolutionary history of the planktic foraminifera. Annu. Rev. Earth Planet. Sci. 2015, 43, 139–166. [Google Scholar] [CrossRef]
  31. Schmidt, D.N.; Thierstein, H.R.; Bollmann, J.; Schiebel, R. Abiotic forcing of plankton evolution in the Cenozoic. Science 2004, 303, 207–210. [Google Scholar] [CrossRef]
  32. Boscolo Galazzo, F.; Giusberti, L.; Luciani, V.; Thomas, E. Paleoenvironmental changes during the Middle Eocene Climatic Optimum (MECO) and its aftermath: The benthic foraminiferal record from the Alano section (NE Italy). Palaeogeogr. Palaeocl. 2013, 378, 22–35. [Google Scholar] [CrossRef]
  33. Jovane, L.; Florindo, F.; Coccioni, R.; Dinarès-Turell, J.; Marsili, A.; Monechi, S.; Roberts, A.P.; Sprovieri, M. The Middle Eocene Climatic Optimum event in the Contessa Highway section, Umbrian Apennines, Italy. Bull. Geol. Soc. Am. 2007, 119, 413–427. [Google Scholar] [CrossRef]
  34. Savian, J.F.; Jovane, L.; Frontalini, F.; Trindade, R.I.F.; Coccioni, R.; Bohaty, S.M.; Wilson, P.A.; Florindo, F.; Roberts, A.P.; Catanzariti, R.; et al. Enhanced primary productivity and magnetotactic bacterial production in response to middle Eocene warming in the Neo-Tethys Ocean. Palaeogeogr. Palaeocl. 2014, 414, 32–45. [Google Scholar] [CrossRef]
  35. Cantalejo, B.; Pickering, K.T.; McNiocaill, C.; Bown, P.; Johansen, K.; Grant, M. A revised age-model for the Eocene deep-marine siliciclastic systems, Aínsa Basin, Spanish Pyrenees. J. Geol. Soc. 2021, 178, 131–172. [Google Scholar] [CrossRef]
  36. Jovane, L.; Sprovieri, M.; Coccioni, R.; Florindo, F.; Marsili, A.; Laskar, J. Astronomical calibration of the middle Eocene Contessa Highway section (Gubbio, Italy). Earth Planet. Sci. Lett. 2010, 298, 77–88. [Google Scholar] [CrossRef]
  37. Živković, S.; Babić, L. Palaeoceanographic implications of smaller benthic and planktonic foraminifera from the Eocene Pazin Basin (Coastal Dinarides, Croatia). Facies 2003, 49, 49–60. [Google Scholar] [CrossRef]
  38. Korbar, T. Orogen evolution of the External Dinarides in the NE Adriatic region: A model constrained by tectonostratigraphy of Upper Cretaceous to Paleogene carbonates. Earth-Sci. Rev. 2009, 95, 296–312. [Google Scholar] [CrossRef]
  39. Vlahović, I.; Tišljar, J.; Velić, I.; Matičec, D. Evolution of the Adriatic carbonate platform: Palaeogeography, main events and depositional dynamics. Paleogeogr. Paleoclimatol. Paleoecol. 2005, 220, 333–360. [Google Scholar] [CrossRef]
  40. Croatian Geological Survey: Geological Map of the Republic of Croatia at the Scale 1:300,000, Department of Geology, Croatian Geological Survey, Zagreb. 2009. Available online: https://www.kig.kartografija.hr/index.php/kig/article/view/158 (accessed on 26 June 2025).
  41. Chester, R. Marine Geochemistry, 2nd ed.; Wiley–Blackwell/Unwin Hyman: London, UK, 2000; pp. 1–520. [Google Scholar]
  42. Ryba, S.A.; Burgess, R.M. Effects of sample preparation on the measurement of organic carbon, hydrogen, nitrogen, sulfur and oxygen concentrations in marine sediments. Chemosphere 2002, 48, 139–147. [Google Scholar] [CrossRef]
  43. Galović, I.; Bajraktarević, Z. Sarmatian biostratigraphy of the Mt. Medvednica at Zagreb based on siliceous microfossils (north Croatia, central Paratethys). Geol. Carpath. 2006, 57, 199–210. [Google Scholar]
  44. Shamrock, J.L.; Munoz, E.J.; Carter, J.H. An improved sample preparation technique for calcareous nannofossils in organic-rich mudstones. J. Nannoplankton Res. 2015, 35, 101–110. [Google Scholar] [CrossRef]
  45. Perch-Nielsen, K. Cenozoic calcareous nannofossils. In Plankton Stratigraphy; Bolli, H.M., Saunders, J.B., Perch-Nielsen, K., Eds.; Cambridge University Press: Cambridge, UK, 1985; pp. 427–554. [Google Scholar]
  46. Galović, I. Sarmatijski Apnencev Nanoplankton, Silikoflagelati in Diatomeje Jugozahodnega Dela Paratetide. Ph.D. Thesis, Universitiy of Ljubljana, Ljubljana, Slovenija, 2009; pp. 1–199. [Google Scholar]
  47. Galović, I. Sarmatian biostratigraphy of a marginal sea in northern Croatia based on calcareous nannofossils. Mar. Micropaleontol. 2020, 161, 101928. [Google Scholar] [CrossRef]
  48. Martini, E. Standard Tertiary and Quaternary calcareous nannoplankton zonation. In Proceedings of the Second Planktonic Conference, Roma, Farinacci, A., Ed. Tecnoscienza 1971, 2, 739–785. [Google Scholar]
  49. Green, O.R. A Manual of Practical Laboratory and Field Techniques in Palaeobiology; Kluwer Academic: London, UK, 2001; pp. 1–538. [Google Scholar]
  50. Ištuk, Ž.; Kampić, Š.; Felja, I.; Pavlović, M.; Tudor, T.; Jazvac, I.; Pezelj, Đ.; Horvat, M.; Čosović, V. Retrieving planktonic foraminifera from lithified rocks, examples from the Eocene limestones and marls (External Dinarides, Croatia). MethodsX 2023, 10, 102233. [Google Scholar] [CrossRef] [PubMed]
  51. Pearson, P.N.; Olsson, R.K.; Hemblen, C.; Huber, B.T.; Berggren, W.A. Atlas of Eocene Planktonic Foraminifera; Cushman Special Publication: Glen Allen, VA, USA, 2006; Volume 41, pp. 1–513. [Google Scholar]
  52. Wade, B.S.; Pearson, P.N.; Berggren, W.A.; Pälike, H. Review and revision of Cenozoic tropical planktonic foraminiferal biostratigraphy and calibration to the geomagnetic polarity and astronomical time scale. Earth-Sci. Rev. 2011, 104, 111–142. [Google Scholar] [CrossRef]
  53. Luterbacher, H.P.; Ali, J.R.; Brinkhuis, H.; Gradstein, F.M.; Hooker, J.J.; Monechi, S.; Ogg, J.G.; Powell, J.; Röhl, U.; Sanfilippo, A.; et al. The Paleogene period. In A Geologic Time Scale; Gradstein, F.M., Ogg, J.G., Smith, A.G., Eds.; Cambridge University Press: Cambridge, UK, 2004; pp. 384–408. [Google Scholar]
  54. Azibeiro, L.A.; Kučera, M.; Jonkers, L.; Cloke-Hayes, A.; Sierro, F.J. Nutrients and hydrography explain the composition of recent Mediterranean planktonic foraminiferal assemblages. Mar. Micropal. 2023, 179, 102201. [Google Scholar] [CrossRef]
  55. Huber, B.T. Planktonic foraminifer biostratigraphy of Campanian–Maestrichtian sediments from Sites 698 and 700, southern South Atlantic. In Proceedings of the Ocean Drilling Program, Scientific Results; Ciesielski, P.F., Kristoffersen, Y., Eds.; Ocean Drilling Program: College Station, TX, USA, 1991; Volume 114, pp. 281–297. [Google Scholar] [CrossRef]
  56. Wade, B.S.; Aljahdali, M.H.; Mufrreh, Y.A.; Memesh, A.M.; Alsoubho, S.A.; Zalmout, I.S. Upper Eocene planktonic foraminifera from northern Saudi Arabia: Implications for stratigraphic ranges. J. Micropalaeontol. 2021, 40, 145–161. [Google Scholar] [CrossRef]
  57. Pettijohn, F.J. Sedimentary Rocks, 2nd ed.; Harper and Row Publishers: New York, NY, USA, 1975; pp. 1–628. [Google Scholar]
  58. Horvat, M.; Tomašić, N.; Aljinović, D.; Bucković, D.; Ćorić, S.; Ćosović, V.; Felja, I.; Galović, I.; Ištuk, Ž.; Kampić, Š.; et al. Eocene Weathering Oscillations Imprinted in Marl Mineral and Geochemical Record (Dinaric Foreland Basin, Croatia). J. Earth Sci. 2025, 36, 1236–1250. [Google Scholar] [CrossRef]
  59. Yurchenko, A.Y. Genesis of Calcite in Carbonates Within Sedimentary Basins According to Carbon and Oxygen Stable Isotopes Distribution; Moscow University Geology Bulletin: Moscow, Russia, 2014; pp. 107–110. [Google Scholar]
  60. Agnini, C.; Fornaciari, E.; Raffi, I.; Catanzariti, R.; Pälike, H.; Backman, J.; Rio, D. Biozonation and biochronology of Paleogene calcareous nannofossils from low and middle latitudes. Newsl. Stratigr. 2014, 47, 131–181. [Google Scholar] [CrossRef]
  61. Agnini, C.; Backman, J.; Boscolo-Galazzo, F.; Condon, D.J.; Fornaciari, E.; Galeotti, S.; Giusberti, L.; Grandesso, P.; Lanci, L.; Luciani, V.; et al. Proposal for the Global Boundary Stratotype Section and Point (GSSP) for the Priabonian Stage (Eocene) at the Alano section (Italy). Episodes 2021, 44, 151–173. [Google Scholar] [CrossRef]
  62. Ogg, J.G. Geomagnetic Polarity Time Scale. In Geologic Time Scale 2020; Gradstein, F.M., Ogg, J.G., Schmitz, M.D., Ogg, G.M., Eds.; Elsevier: Amsterdam, The Netherlands, 2020; pp. 159–192. [Google Scholar] [CrossRef]
  63. Berggren, W.A.; Kent, D.V.; Swisher III, C.C.; Aubry, M.-P. A Revised Cenozoic Gochronology and Chronostratigraphy. In Geochronology Time Scales and Global Stratigraphic Correlation; Berggren, W.A., Kent, D.V., Aubry, M.-P., Hardenbol, J., Eds.; SEPM: Tulsa, OK, USA, 1995; pp. 129–211995. [Google Scholar]
  64. Okada, K.H.; Bukry, D. Supplementary modifications and introduction of code numbers to the low latitude coccolith biostratigraphic zonation. Mar. Micropaleontol. 1980, 5, 321–325. [Google Scholar] [CrossRef]
  65. Živković, S.; Glumac, B. Paleoenvironmental reconstruction of the Middle Eocene Trieste-Patin Basin (Croatia) from benthic foraminiferal assemblages. Micropaleontology 2007, 53, 285–310. [Google Scholar] [CrossRef]
  66. Berggren, W.A.; Pearson, P.N. A revised tropical to subtropical Paleogene planktonic foraminiferal zonation. J. Foraminifer. Res. 2005, 35, 279–298. [Google Scholar] [CrossRef]
  67. Dickens, G.R. The blast in the past. Nature 1999, 401, 752–755. [Google Scholar] [CrossRef]
  68. Spofforth, D.J.A.; Agnini, C.; Pälike, H.; Rio, D.; Fornaciari, E.; Giusberti, L.; Luciani, V.; Lanci, L.; Muttoni, G. Organic carbon burial following the Middle Eocene Climatic Optimum in the central western Tethys. Paleoceanography 2010, 25, 1–11. [Google Scholar] [CrossRef]
  69. Alegret, L.; Arreguin-Rodriguez, G.J.; Travina-Moreno, C.A.; Thomas, E. Turnover and stability in deep sea benthic foraminifera as tracers of Paleogene global changes. Glob. Planet. Change 2021, 196, 103372. [Google Scholar] [CrossRef]
  70. Gebhardt, H.; Ćorić, S.; Darga, R.; Briguglio, A.; Achenk, B.; Werner, W.; Andersen, N.; Sames, B. Middle to Late Eocene paleoenvironmental changes in a marine transgressive sequence from the northern Tethyan margin (Adelholzen, Germany). Aust. J. Earth Sci. 2013, 106, 45–72. [Google Scholar]
  71. Pearson, P.N.; Ditchfield, P.W.; Singano, J.; Harcourt-Brown, K.G.; Nicholas, C.J.; Olsson, R.K.; Shackleton, N.J.; Hall, M.A. Warm tropical sea surface temperatures in the Late Cretaceous and Eocene epochs. Nature 2001, 413, 481–487. [Google Scholar] [CrossRef] [PubMed]
  72. Pejnović, I.; Luciani, V.; Ćosović, V. Connecting morphological changes in planktonic foraminifera to Late Eocene cooling: A case study on Pseudohastigerina micra (Cole 1927) from the Dinaric foreland basin Adriatic Sea. Micropaleontology 2025, 71, 235–252. [Google Scholar] [CrossRef]
  73. Ćosović, V.; Drobne, K.; Moro, A. Paleoenvironmental model from Eocene foraminiferal limestones of the Adriatic carbonate platform (Istrian Peninsula). Facies 2004, 50, 61–75. [Google Scholar] [CrossRef]
  74. Kearns, L.E.; Bohaty, S.M.; Edgar, K.M.; Nogué, S.; Ezard, T.H.G. Searching for function: Reconstructing adaptive niche changes using geochemical and morphological data planktonic foraminifera. Front. Ecol. Evol. 2021, 9, 679–722. [Google Scholar] [CrossRef]
  75. Aubry, M.-P. Late Paleogene calcareous nannoplankton evolution: A tale of climatic deterioration. In The Eocene-Oligocene Climatic and Biotic Changes; Prothero, D., Berggren, W.A., Eds.; Princeton University Press: Princeton, NJ, USA, 1992; pp. 272–309. [Google Scholar] [CrossRef]
  76. Toffanin, F.; Agnini, C.; Fornaciari, E.; Rio, D.; Giusberti, L.; Luciani, V.; Spofforth, D.J.A.; Pälike, H. Changes in calcareous nannofossil assemblages during the Middle Eocene Climatic Optimum: Clues from the central-western Tethys (Alano section, NE Italy). Mar. Micropaleontol. 2011, 81, 22–31. [Google Scholar] [CrossRef]
  77. Bralower, T.J. Evidence of surface water oligotrophy during the Paleocene-Eocene thermal maximum: Nannofossil assemblage data from Ocean Drilling Program Site 690, Maud Rise, Weddell Sea. Paleoceanography 2002, 17, 13-1–13-12. [Google Scholar] [CrossRef]
  78. Cachão, M.; Moita, M.T. Coccolithus pelagicus, a productivity proxy related to moderate fronts off Western Iberia. Mar. Micropaleontol. 2000, 39, 131–155. [Google Scholar] [CrossRef]
  79. Rahman, A.; Roth, P.H. Late Neogene paleoceanography and paleoclimatology of the Gulf of Aden region based on calcareous nannofossils. Paleoceanography 1990, 5, 91–107. [Google Scholar] [CrossRef]
  80. Prista, G.; Narciso, Á.; Cachão, M. Coccolithus pelagicus subsp. braarudii morphological plasticity in response to variations in the Canary region upwelling system over the past 250 ka. Clim. Past Discuss. 2023, 2023, 1–22. [Google Scholar] [CrossRef]
  81. Sharma, N.; Spangenberg, J.E.; Adatte, T.; Vennemann, T.; Kocsis, L.; Vérité, J.; Valero, L.; Castelltort, S. Middle Eocene Climatic Optimum (MECO) and its imprint in the continental Escanilla Formation, Spain. Clim. Past. 2024, 20, 935–949. [Google Scholar] [CrossRef]
  82. Peñalver-Clavel, I.; Agnini, C.; Westerhold, T.; Cramwinckel, M.J.; Dallanave, E.; Bhattacharya, J.; Sutherland, R.; Alegret, L. Integrated record of the Late Lutetian Thermal Maximum at IODP site U1508, Tasman Sea: The deep-sea response. Marine Micropaleontol. 2024, 191, 102390. [Google Scholar] [CrossRef]
  83. Waide, R.B.; Willig, M.R.; Steiner, C.F.; Mittelbach, G.; Gough, L.; Dodson, S.I.; Juday, G.P.; Parmenter, R. Less. The relationship between productivity and species richness. Annu. Rev. Ecol. Syst. 1999, 30, 257–300. [Google Scholar]
  84. Giorgioni, M.; Jovane, L.; Rego, E.S.; Rodelli, D.; Frontalini, F.; Coccioni, R.; Catanzariti, R.; Özcan, E. Carbon cycle instability and orbital forcing during the Middle Eocene Climatic Optimum. Sci. Rep. 2019, 9, 9357. [Google Scholar] [CrossRef]
  85. Boulila, S.; Laskar, J.; Haq, B.U.; Galbrun, B.; Hara, N. Long-term cyclicities in Phanerozoic sea-level sedimentary record and their potential drivers. Glob. Planet. Change 2018, 165, 128–136. [Google Scholar]
  86. Raffi, I.; Agnini, C.; Backman, J.; Catanzariti, R.; Pälike, H. A Cenozoic calcareous nannofossil biozonation from low and middle latitudes: A synthesis. J. Nannoplankton Res. 2016, 36, 121–132. [Google Scholar]
  87. Rodelli, D. Paleoceanographic Variations Through the Study of Rock Magnetic Properties: Biogenic Magnetite as a New Paleoenvironmental Indicator. Ph.D. Thesis, Universidade de São Paulo, São Paulo, Brazil, 2018. [Google Scholar]
  88. Wade, B.S.; Bown, P.R. Calcareous nannofossils in extreme environments: The Messinian Salinity Crisis, Polemi Basin, Cyprus, Paleogeogr. Paleoclimatol. Paleoecol. 2006, 223, 271–286. [Google Scholar] [CrossRef]
  89. Narciso, A.; Cachao, M.; de Abreu, L. Coccolithus pelagicus subsp. pelagicus versus Coccolithus pelagicus subsp. braarudii (Coccolithophore, Haptophyta): A proxy for surface subarctic Atlantic waters off Iberia during the last 200 kyr. Mar. Micropaleontol. 2006, 59, 15–34. [Google Scholar] [CrossRef]
  90. Bijma, I.; Faber, W.W.; Helminen, C. Temperature and salinity limits for growth and survival of some planktonic foraminifers in laboratory culture. J. Foraminifer. Res. 1990, 20, 95–116. [Google Scholar] [CrossRef]
  91. Juggins, S. C2 Software for Ecological and Palaeoecological Data Analysis and Visualisation; Newcastle University: Newcastle upon Tyne, UK, 2007; p. 73. [Google Scholar]
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Figure 1. (a) Location of the Istrian Peninsula and the studied sections (https://maps-for-free.com, accessed on 11 January 2024). (b) Simplified palaeogeographical map of the central Neotethys region for the Eocene (with present-day geographic lineaments after [38]. The Adriatic–Dinaric domain corresponds to the spatial distribution of the Mesozoic Adriatic–Dinaric carbonate platform (according to [39]). (c) Geological map of the Istrian Peninsula showing the studied locations (Croatian Geological Survey, 2009) [40].
Figure 1. (a) Location of the Istrian Peninsula and the studied sections (https://maps-for-free.com, accessed on 11 January 2024). (b) Simplified palaeogeographical map of the central Neotethys region for the Eocene (with present-day geographic lineaments after [38]. The Adriatic–Dinaric domain corresponds to the spatial distribution of the Mesozoic Adriatic–Dinaric carbonate platform (according to [39]). (c) Geological map of the Istrian Peninsula showing the studied locations (Croatian Geological Survey, 2009) [40].
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Figure 2. Stratigraphical distribution of calcareous nannofossils in the investigated sections alongside the regional subzones [15] and global zones [48].
Figure 2. Stratigraphical distribution of calcareous nannofossils in the investigated sections alongside the regional subzones [15] and global zones [48].
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Figure 3. Microphotographs of selected calcareous nannofossil species from the Racaniand Jakomići sections. (1–4) Sphenolithus spiniger Bukry, 1971 (sample J2). (5,6) Sphenolithus moriformis (Brönnimann and Stradner, 1960) Bramlette and Wilcoxon, 1967; (sample RAC2d). (7,8) Sphenolithus radians Deflandre in Grassé, 1952 (sample J2). (9) Sphenolithus furcatolithoides Locker, 1967 (sample J2). (10) Zygrhablithus bijugatus (Deflandre in Deflandre and Fert, 1954) Deflandre, 1959 (sample J2). (11) Zygrhablithus bijugatus (Deflandre in Deflandre and Fert, 1954) Deflandre, 1959 (sample RAC 2d). (12,13) Calcidiscus bicircus Bown, 2005 (sample J2). (14) Cyclicargolithus floridanus (Roth and Hay in Hay et al., 1967) Bukry, 1971 (sample J2). (15) Reticulofenestra producta (Kamptner, 1963) Varol, 1989 (sample J2). (16) Discoaster barbadiensis Tan Sin Hok, 1927 (sample RAC 2d). (17) Coccolithus pelagicus (Wallich, 1877) Schiller, 1930 (sample J2). (18) Clausicoccus fenestratus (Deflandre and Fert, 1954) Prins, 1979 (sample JAK 3). (19) Coccolithus formosus (Kamptner, 1963) Wise, 1973 (sample RAC 2d). (20) Helicosphaera bramlettei (Müller, 1970) Jafar & Martini, 1975 (sample J2). (21) Lanternithus minutus Stradner, 1962 (sample RAC 2d). (22) Pontosphaera multipora (Kamptner, 1948 ex Deflandre in Deflandre and Fert, 1954) Roth, 1970 (sample RAC 2d). (23) Blackites inversus (Bukry and Bramlette, 1969) Bown and Newsam, 2017 (sample J2). (24) Blackites tenuis (Bramlette and Sullivan, 1961) Sherwood, 1974 (sample RAC 2d). (25) Blackites stilus Bown, 2005 (sample JAK3). (26) Coccolithus eopelagicus (Bramlette and Riedel, 1954) Hay, Mohler, and Wade, 1966 (sample RAC 2d). (27) Reticulofenestra umbilicus (Levin, 1965) Martini and Ritzkowski, 1968 (sample RAC 2d). (28) Reticulofenestra dictyoda (Deflandre in Deflandre and Fert, 1954) Stradner in Stradner and Edwards, 1968 (sample RAC 2d). (29) Chiasmolithus solitus (Bramlette and Sullivan, 1961) Locker, 1968 (sample J2). (30,31) Umbilicosphaera bramlettei (Hay and Towe, 1962) Bown et al., 2007 (sample J2). (32) Braarudosphaera bigelowii (Gran & Braarud 1935) Deflandre, 1947 (sample RAC 5). Scale bars = 5 µm (for 1–22) and scale bars = 10 µm (for 23–32).
Figure 3. Microphotographs of selected calcareous nannofossil species from the Racaniand Jakomići sections. (1–4) Sphenolithus spiniger Bukry, 1971 (sample J2). (5,6) Sphenolithus moriformis (Brönnimann and Stradner, 1960) Bramlette and Wilcoxon, 1967; (sample RAC2d). (7,8) Sphenolithus radians Deflandre in Grassé, 1952 (sample J2). (9) Sphenolithus furcatolithoides Locker, 1967 (sample J2). (10) Zygrhablithus bijugatus (Deflandre in Deflandre and Fert, 1954) Deflandre, 1959 (sample J2). (11) Zygrhablithus bijugatus (Deflandre in Deflandre and Fert, 1954) Deflandre, 1959 (sample RAC 2d). (12,13) Calcidiscus bicircus Bown, 2005 (sample J2). (14) Cyclicargolithus floridanus (Roth and Hay in Hay et al., 1967) Bukry, 1971 (sample J2). (15) Reticulofenestra producta (Kamptner, 1963) Varol, 1989 (sample J2). (16) Discoaster barbadiensis Tan Sin Hok, 1927 (sample RAC 2d). (17) Coccolithus pelagicus (Wallich, 1877) Schiller, 1930 (sample J2). (18) Clausicoccus fenestratus (Deflandre and Fert, 1954) Prins, 1979 (sample JAK 3). (19) Coccolithus formosus (Kamptner, 1963) Wise, 1973 (sample RAC 2d). (20) Helicosphaera bramlettei (Müller, 1970) Jafar & Martini, 1975 (sample J2). (21) Lanternithus minutus Stradner, 1962 (sample RAC 2d). (22) Pontosphaera multipora (Kamptner, 1948 ex Deflandre in Deflandre and Fert, 1954) Roth, 1970 (sample RAC 2d). (23) Blackites inversus (Bukry and Bramlette, 1969) Bown and Newsam, 2017 (sample J2). (24) Blackites tenuis (Bramlette and Sullivan, 1961) Sherwood, 1974 (sample RAC 2d). (25) Blackites stilus Bown, 2005 (sample JAK3). (26) Coccolithus eopelagicus (Bramlette and Riedel, 1954) Hay, Mohler, and Wade, 1966 (sample RAC 2d). (27) Reticulofenestra umbilicus (Levin, 1965) Martini and Ritzkowski, 1968 (sample RAC 2d). (28) Reticulofenestra dictyoda (Deflandre in Deflandre and Fert, 1954) Stradner in Stradner and Edwards, 1968 (sample RAC 2d). (29) Chiasmolithus solitus (Bramlette and Sullivan, 1961) Locker, 1968 (sample J2). (30,31) Umbilicosphaera bramlettei (Hay and Towe, 1962) Bown et al., 2007 (sample J2). (32) Braarudosphaera bigelowii (Gran & Braarud 1935) Deflandre, 1947 (sample RAC 5). Scale bars = 5 µm (for 1–22) and scale bars = 10 µm (for 23–32).
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Figure 4. Bulk carbonate stable isotope δ13C signatures of the samples with positions of (bio)events (1–4) in the sections from Istria compared with regional (Mediterranean) and global data. Biostratigraphic events are modified according to [3,60,61] with the calibrated data at GTS12. The newest geomagnetic polarity time scale in [62] (GTS20) is plotted on the left. The orange colour represents CIE phase of the LLTM and MECO, while yellow represents the pre- and post-MECO phases.
Figure 4. Bulk carbonate stable isotope δ13C signatures of the samples with positions of (bio)events (1–4) in the sections from Istria compared with regional (Mediterranean) and global data. Biostratigraphic events are modified according to [3,60,61] with the calibrated data at GTS12. The newest geomagnetic polarity time scale in [62] (GTS20) is plotted on the left. The orange colour represents CIE phase of the LLTM and MECO, while yellow represents the pre- and post-MECO phases.
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Figure 5. Overview of the biostratigraphic data with the foraminiferal biozonation of (P) [53] (E, middle column) [63] and (E) [52], respectively, the global nannofossil zonations of (NP) [48], (CP) [64] and (CNE) [60] and the regional zonation of (MNP) [15] through the thermal events. Regional subzones are marked in darker shades of blue, with the main and secondary biohorizons detected in the sections.
Figure 5. Overview of the biostratigraphic data with the foraminiferal biozonation of (P) [53] (E, middle column) [63] and (E) [52], respectively, the global nannofossil zonations of (NP) [48], (CP) [64] and (CNE) [60] and the regional zonation of (MNP) [15] through the thermal events. Regional subzones are marked in darker shades of blue, with the main and secondary biohorizons detected in the sections.
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Table 1. Concentration of selected geochemical parameters important to interpretating paleoenvironmental conditions from the Racani and Jakomići samples. Methods used are described in chapter 2.1.
Table 1. Concentration of selected geochemical parameters important to interpretating paleoenvironmental conditions from the Racani and Jakomići samples. Methods used are described in chapter 2.1.
RAC 2cJ3
TOT/C (%)7.256.77
TOT/S (%)0.290.02
Total C%7.516.97
TOC%0.110.13
TIC%7.16.59
N%0.030.04
Insolble residum (%)41.0437.72
Al2O3 (wt %)7.017.99
TiO2 (wt %)0.340.4
Mn0.120.08
Fe2.112.41
Sr (ppm)686.6699.9
Ba (ppm)247176
Th (ppm)4.45.2
U (ppm)1.41.4
Th/U3.143.71
Sr/Ba2.783.98
CaCO3 (wt %)61.8655.41
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Galović, I.; Pezelj, Đ.; Lukić, R.; Mužek, K.; Petrinjak, K.; Horvat, M.; Ćosović, V. Record of Mid-Eocene Warming Events in the Istrian Paleogene Basin, Neotethys (Outer Dinarides, Croatia). Geosciences 2025, 15, 366. https://doi.org/10.3390/geosciences15090366

AMA Style

Galović I, Pezelj Đ, Lukić R, Mužek K, Petrinjak K, Horvat M, Ćosović V. Record of Mid-Eocene Warming Events in the Istrian Paleogene Basin, Neotethys (Outer Dinarides, Croatia). Geosciences. 2025; 15(9):366. https://doi.org/10.3390/geosciences15090366

Chicago/Turabian Style

Galović, Ines, Đurđica Pezelj, Renata Lukić, Katja Mužek, Krešimir Petrinjak, Marija Horvat, and Vlasta Ćosović. 2025. "Record of Mid-Eocene Warming Events in the Istrian Paleogene Basin, Neotethys (Outer Dinarides, Croatia)" Geosciences 15, no. 9: 366. https://doi.org/10.3390/geosciences15090366

APA Style

Galović, I., Pezelj, Đ., Lukić, R., Mužek, K., Petrinjak, K., Horvat, M., & Ćosović, V. (2025). Record of Mid-Eocene Warming Events in the Istrian Paleogene Basin, Neotethys (Outer Dinarides, Croatia). Geosciences, 15(9), 366. https://doi.org/10.3390/geosciences15090366

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